The role of coincident site lattice boundaries during selective growth in interstitial-free steels
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I.
INTRODUCTION
THE recrystallization of cold-rolled steels is generally considered to take place by the sequential operation of nucleation and growth processes, t'~ In the case of interstitialfree (IF) steels, the occurrence of selective growth has been modeled in terms of the preferential migration of E (110) boundaries. ~21Here, "transformation" or "rotation" is assumed to occur solely about the (110) axes that are perpendicular to the most active {110} slip planes. This mechanism is attractive because it rotates the grains belonging to the (110)[JRD (rolling) fiber into the (11 I)[]ND (annealing) fiber.pI It has also been shownt4.5,61that nucleation in such heavily rolled steels takes place primarily in regions of high Taylor factor, i.e., of high stored energy, with a threshold Taylor factor (stored energy) below which nucleation does not occur. These observations, together with data on more lightly rolled electrical steelst71 form the basis for a generalized "nucleation and growth" model for texture change during recrystallization that has been proposed recently.[6,8~ This analysis features the {110} plane matching growth mechanism of Watanabe, t91 which does not distinguish between non-coincident site lattice (CSL) and CSL misorientations, and permits growth to occur as long as the misorientation axis between the nucleus and matrix coincides with a (110) axis. However, observations on single crystals and bicrystals by Aust and Rutter~~ have shown that boundary migration can be more rapid when the nucleus-matrix misorientation satisfies one of the CSL conditions, i.e., when the misorientation is not a random one. The previously mentioned
PETER GANGLI, Chemical Engineer, is with FE2000 Inc., Vaudreuil, PQ, Canada J7V 8P5. LEO KESTENS, Research Associate, is with the Department of Flat Rolling, Center for Research in Metallurgy, B-9052 Gent, Belgium. JOHN J. JONAS, Birks Professor of Metallurgy, is with the Department of Metallurgical Engineering, McGill University, Montreal, PQ, Canada H3A 2A7. Manuscript submitted October 5, 1995. 2178--VOLUME 27A, AUGUST 1996
modelrr.sI was therefore modified to allow recrystallization to take place solely by means of selected CSL transformations.[~u Here, this approach is considered in more detail and distinctions are drawn, not only between random and CSL boundaries, but also between competing CSL relationships. In this way, the rotations likely to play significant roles during recrystallization are identified, together with those that make much smaller contributions. Some attention is also paid to the possible role of E (111) rotations during recrystallization. I1.
EXPERIMENTAL PROCEDURE
A. Materials and Experimental Conditions In this investigation, texture data were analyzed for two steels that had previously been studied by other authors. I2,~zl The first was a Ti-Nb stabilized IF steel with a composition of 0.0018 pct C, 0.02 pct Si, 0.14 pct Mn, 0.004 pct P, 0.003 pct S, 0.042 pct A1, 0.0023 pct N, 0.079 pet Ti, and 0.010 pct Nb. It was cold rolled to 85 pct re
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